Helicopter



C. G. PULLIN May 30, I950 HELICOPTER l0 Sheets-Sheet 1 Filed May 20, 1944 4 ENE HS C. G. PULLIN HELICOPTER May 30, 1950 10 Sheets-Sheet 2 Filed May 20, 1944 C. G. PULLIN HELICOPTER May 30, 1950 10 Sheets-Sheet 3 Filed May 20, 1944 wswws \QQ s 0. s. PULLIN May 30, 1950 HELICOPTER l0 Sheets-Sheet 4 Filed May 20, 1944 M1 W14; 51 W? W ATTURMEYS y 1950 c. G. PULLIN 2,509,313

HELICOPTER Filed May 20, 1944 10 Sheets-Sheet 5 C. G. PULLIN May 30, 1950 HELICOPTER l0 Sheets-Sheet 6 Filed May 20, 1944 C. G. PULLIN HELICOPTER May 30, I950 10 Sheets-Sheet 7 Filed May 20, 1944 Em; gg g mm a ATI'ORNEYS May 30, 1950 PULLIN 2,509,313

HELICOPTER Filed May 20, 1944 10 Sheets-Sheet 8 ITTMME Y5 May 30, 1950 c, PULLlN 2,509,313

HELICOPTER Filed May 20, 1944 10 Sheets-Sheet 9 2M 15/ 4 M 16/17? 170 149 w r ATTOKNE Y5 Patented May 30, 1950 UNITED STATES PATENT OFFICE 2,509,313 HELICOPTER Cyril George Pullin,

Wimbledon,

London, England, assignor to The Cierva Autogiro Company Limited,

Application May 20, 1944, Serial No.

London, England, a British company In Great Britain May 18, 1943 Section 1, Public Law Patent expires 11 Claims. (Cl. INF-169.56)

This invention relates to helicopters having one or more torsional flapping rotors with stable characteristic, the last-named terms being defined as under:

Two further terms, which will be hereinafter used. are defined as under:

"Tilting hub"=a rotor hub whose (non-rotative) axis member is connected to the airframe by means of a gimbal or universal joint;

"Direct control=a system employing a connection between the axle member and the flying controls, whereby the position of the latter regulates the magnitude and direction of the inthe axle member from its neutral position.

I have found that advantages are to be gained in a helicopter having a torsional flapping rotor, especially in lightness of and response to the controls, by using a higher ratio of pitch change amplitude to flapping angle than hitherto has been usual, but this introduces additional problems.

If the said ratio is, for instance, 4 to 1, i. e. a flapping displacement of 1 gives rise to a pitch change of 4, and the normal mean pitch angle In a torsional flapping rotor with the abovementioned pitch change/flapping ratio and with a tilting hub and direct control, a sudden control movement sufllcient to tilt the hub through more than 2 from its previous position may cause stalling of the blades, because the 690, August 8, 1946 May 18, 1968 already in high speed level (forward) flight, into a dive. In such a case a control movement giving an initial tilt to the hub (from its previous position) of less than 2 may cause stalling of the blades.

stalling of the blades directly controlled tilting The invention therefore is not limited to rotors with a directly controlled tilting hub but is applicable to any helicopter having a torsional flapping nounced torsional flapping characteristic, 1. e. in which the pitch increase for a given downward flapping angle is at least greater than 1.

A principal object of the the advantage of large ratio of pitch change to small limit in the downward direction.

Broadly, this object is achieved in the present invention by providing rotor blade mounting articulations which are characterised by a compound pivot arrangement incorporating limit stops, which confine the torsional-flapping charplacement, while permitting more extended flapping movements to occur without further change of pitch angle, degree of pitch with such an arrangement downward flapping of the blade from its neutral position will be accompanied by increase of pitch angle in the predetermined ratio until a certain limit is reached, at which in normal conditions the actual incidence of the blade is still well below the stalling angle; further downward flapping displacement is not prevented, but it is not attended by any large increase of pitch angle, which remains constant (or nearly so) at or near its limitin (maximum) value. The arrangement is preferably such that similar conditions apply to upward flapping, principally because if it were not so, an unsymmetrical oscillation of pitch angle would occur whenever the amplitude of the flapping oscillation should exceed the value at which the pitch angle reaches its limiting value (either maximum or minimum). In other words, in order that symmetry 0! the pitch angle oscillation may be preserved, regardless of the amplitude of flapping oscillation, it is desirable that the range of flappin angles over which pronounced torsional-flapping characteristics obtain be symmetrically distributed about the neutral position of the blade corresponding to the mean coning angle averaged over all normally encountered flight conditions. In this connexion it can be shown that with a rotor having torsional-flappin characteristics whose pitch change/flapping angle ratio is large, 1. e. 4: unity, the ooning angle is substantially constant for varyin p wer input.

The more extended ranges of upward and downward flapping associated with constant or nearly constant pitch angle must have some limit set to them by mechanical stop means, but as these limits will be dictated by conditions irrelevant to the flapping oscillation, e. g. permissible droop angle at rest and prevention of a blade blowing right up in a wind when not rotating, there is no need for these limits to be symmetricall! disposed about the neutral position of the blade; generally speaking, it will be convenient for the downward flapping angle to have a smaller ultimate limit than the upward flappin angle.

More particularly, the rotor blade-mounting articular assembly may comprise an articulation having relatively pronounced torsional-flapping characteristics, stops limiting movement on such articulation in either direction, and an additional flapping pivot or pivots giving no or very little pitch change with flapping and permitting greater range of flapping movement than the torsionaliiapping articulation, the arrangement being such that movement on the auxiliary flapping pivot or pivots will only occur when the blade has reached one or other of the stops limiting movement on the torsional-flapping articulation.

One way of achievin the last-named condition is to utilise centrifugal force by oifsetting the axes of the auxiliary flapping pivots, of which two are provided, above and below the blade axis, and providing means which ensure that upward flapping place about the lower auxiliary pivot and vice versa: flapping about the auxiliary pivots is therefore always resisted by centrifugal force. The oflsets are such that the centrifugal restoring moments about the auxiliary pivots are greater than that about the torsional-flapping articulation, so that flapping dis lacements within the range accommodated by the torsional-flapping articulation will be so acoommodated without movement about the auxilor at least with much reduced iary pivots, which will only come into play for larger displacements.

Alternatively, the rotor blade-mountin articuping pivot and a torsional pivot, stop means limiting blade movement about the torsional pivot but not about the flappin pivot and interconnecting elements includin a yieldable device, incorporating a spring, ensuring that movement on the flapping pivot is accompanied by movement about the torsional pivot in the ap ropriate sense for giving a stable characteristic, until the limits imposed by the said step means are reached, but capable of then yielding to allow more extended displacement (in either direction) about the flapping pivot (without further displacement about the torsional pivot).

In the foregoing statement and the terms torsional pivot" in what follows, and flapping pivot a but may partake in a minor or/and lead/lag displacement," and "a pivot on which displacement is mainly flappin but may partake in a minor degree of torsional or lead/lag displacement."

If independent and the blade supporting member or between two components of the latter, so that drag displacements do not aifect the pitch an le of the blades.

How the foregoing objects others which will hereinafter appear, will be understood from the following description with reference to the accompanying drawings of two typical embodiments of the invention, the scope of which is defined in the appended claims.

In the drawings:

Figure l is a somewhat diagrammatic view in side elevation, partly in section, of a helicopter embodying the invention;

Figure 2 is a view in longitudinal vertical section of the rotor huh and attachments of one rotor blad are attained, and

view in section taken along the line 3-4 of Figure 2;

Figure 3a is a view in elevation of shown in Figure 3.

Figures 4, 4a and 5 are detail views in elevation of parts shown in Figure 8;

Figure 6 is a somewhat diagrammatic view in side elevation of the pilot's control connections;

Figure 'l is a diagrammatic view of the same in perspective;

Figure 8 is a view in longitudinal vertical section of the control housing" (shown at $5 in Figure 6);

Figure 9 is a view in section taken along the line 8-! of Figure 8;

Figure 10 is a somewhat diagrammatic representation in sectional elevation of the rotor hub and one rotor blade root of an alternative embodiment of the invention:

Figure 11 is part sectional plan view of the same (also somewhat diagrammatic);

Figures 12 to 15 are somewhat diagrammatic views of the blade articular mounting of the same, Figure 12 being in elevation, Figure 13 in plan, Figure 14 being in section taken along the line "-44 of Figure 12 and Figure 15 in section taken along the line lB-ll of Figure 14;

mgures18,l7and1Bareentirelyd|agramma l views in elevation indicating the limits of diaccrtain parts placement of the blade about its articular mounting Referring to Figure 1, the helicopter includes a body 2|, undercarriage elements 22, elevator 23, vertical fin 24 and rudder 25. Within the body is mounted the engine 20, which drives the rotor through gears contained in gear boxes 21, 29 and a transmission shaft 20. The final drive shaft is contained in a casing 30 forming an extension of the gear box 29.

The rotor hub is shown at 3i and the lifting rotor blades at 32.

Referring now to Figs. 2, 3, 4 and 5, the casing 30 of Figure 1 is extended upwardly by a hollow support member 30 terminating in a forked end 04 which supports a gimbal ring 35; this in turn supports a hollow axle member 36.

The gimbal ring 35 is provided with four equally spaced inwardly projecting bosses 31 carrying trunnions 38 provided with ball bearings 00. One pair of trunnions articulates with the ends of the supporting fork 34 and the other pair of trunnions with the axle member 36, on which the hub ii is rotatably mounted by means of ball bearings 40, 4|.

The rotor in this example has three blades, to support which the hub is provided with three pairs of cars 42 housing needle bearings 43, in which drag pivot pins 44 are rotatable. Drag links 40 are secured by taper pins 5 to the pins 44. Lead/lag displacements of the rotor blades are accommodated by movement of the drag links and pivot pins relatively to the hub cars 42.

Secured by taper pins 41 in the drag link 45 is a flapping pivot pin 40 and rotatably mounted thereon by means of needle bearings 40 is a blade root supporting link 50 on which the blade is rotatably mounted for torsional, i. e. pitch varying, displacement by means of a ball thrust bearing 52, a preload bearing 53 and a preload nut 54. The main spar of the blade (32) is shown at 55 and is screwed into a blade root housing 5i which is supported on the bearings 52, 53.

In order to obtain the stable torsional/flappin characteristic, the torsional and flapping displacements of the blade are made interdependent by means of a linkage comprising a lever 58 secured to the blade and an arm Ill, 02, lying approximately parallel to the blade and on the leading side thereof, and secured to the flapping pivot pin. This construction i shown in Figures 3, 3a, 4 and 5.

A pair of lugs 56 integral with the spar 55 carries pivot studs 51 on which the lever 50, which is forked, articulates. The forward end of this lever carries studs 59 with spherical seatings which engage a ball 80 formed on the end of the arm part 5| the other end of the latter is tapered to fit in a taper socket of a boss 63 formed on the arm part 62, being secured by a nut 04. The inboard end of the arm part 62 is forked and the fork ends engage trunnions 65 formed on a collar 66, the further connections of which are as follows: Within the flapping pivot pin 40, which is hollow, is a loose sleeve I30 having a flanged end I40, which is secured by bolts 01 to the collar 66 and to a cam plate Ill having face cams I42 engaging corresponding face cams formed in the adjacent end of the flapping pivot pin 40. These cams are shown in elevation in Figure 3a. The weather shield, shown in cross-section in Figure 3, has been omitted from Figure 3a, so as to expose the parts usually protected by it. The cams are held in engagement by the pressure of a spring I which abuts on an internal shoulder I43 of the sleeve I the other end of the spring being retained by the head I of a rod I40 whose other end is secured by a pin I" to a cap Ill,

which retains a stop collar I50. The latter is 5 slidably, but non-rotatably, mounted on the sleeve I39, which is splined at I40 to engage corresponding splines of a sleeve extension of the stop collar I50; said sleeve extension is rotatable in the bore of the flapping pivot pin 40.

Referring to Figure 4a, the stop collar I50 has two slots I5l in its circumference which engage stop lugs I52 formed integrally on the rear face of the blade-supporting link 50. A clearance is established between the stop lugs I52 and ends of the slots I5I, allowing a predetermined amount of relative movemen This arrangement operates as follows:

When the blade is in its mean position, as regards flapping, i. e. there is no flapp g. the collar 66 carrying the arm GI, 52, is locked to the flapping pivot pin, by the action of spring I holding the cam faces I42 in engagement. For small amplitudes of flapping this condition also holds good; the outboard-end 00 of the arm 6|, it being stationary, the lever 50 operates to rotate the blade about the axis of the torsional pivot 50, 52, 54, 5|, in the direction to decrease the blade pitch angle with upward flapping, thus giving a stable torsional/flapping characteristic.

But when the amplitude of flapping is great enough for the clearance between either end of the slots I 5| and the stop lugs I52 to be taken up, any further increase of flapping amplitude causes the stop collar I50 to rotate with the blade-supporting link 50 about the flapping pivot pin 48, and with it the sleeve I30, collar 60 and arm BI, 62, the spring I yielding suiiiciently to allow the cam faces I42 to ride over one another. In such further flapping displacement,

therefore, the arm GI, 52 follows the blade and no further displacement of the blade about the torsional pivot axis takes place. The sto collar I and stop lugs I52 thus serve to limit the amplitude over which the torsional/flapping 5 characteristic obtains and are preferably so set that the positive and negative limits of pitch angle variation (from the mean value) are equal and within the limits required to prevent stalling of the blades. The actual values of these I50 limits depend on the ratio of pitch change to flapping angle, which is approximately equal to the ratio of lengths of the lever 50 and the arm GI, 62. In the example illustrated this ratio is about 5/3, but may be varied by the use of interchangeable arm parts 62, 53 of different lengths as indicated in chain dotted lines.

Limitation of upward and downward flapping is provided by means of a stop plate 60, formed integrally with the drag link 06 and having upper 00 and lower faces 60, 10 which engage the inner surface H of the blade-supporting link 50.

The amplitude limits of flapping imposed by this stop device are much larger than the amplitude limits of torsional flapping imposed by the 05 stop collar I50 and stop lugs I52 and are not necessarily equal for upward and downward flapping. They are dictated principally by the permissible upward flapping argle to prevent damage to the mechanism in gusts when the rotor 70 is not rotating and the permissible droop angle of the blades at rest: The upward limit will in general be greater than the downward limit.

Referring now to Figures 6 to 9. showing the control mechanism of the tilting hub, the pilot's ll seat is indicated at 12. In the conventional positionisacontroleolumnfl pivotedatfltoa crank1lintegralwitharockingshait16suhportedinabearingliandcarryingasproc et 16. The control column is also pivoted at 19 to a push-pull rod 66 actuatin a crank 8| carrying a sprocket 62.

A chain or cable I! is passed over sprocket 18 and over another sprocket ll which is fast on a further sprocket 66.

Similarly a chain or cable ll connects sprocket 62 with a sprocket 6! fast on yet another sprocket 66. Sprockets ll, l6, I9, 66 are coaxial as shown in Figure 6, but for convenience in following the run of the controls the pairs of sprockets ll, 65 and It, 66 respectively are shown in Figure 'I with their axes separated.

Sprocket 66 carries a chain or cable 66 which is also passed over a sprocket 61 within a control housing 65, while another sprocket 6! within this housing (see Figure 8) is actuated by a chain m cable 9| which is passed over sprocket II.

The chains or cables 66, 9| are also passed over four jockey pulleys 93 (indicated diagrfl matically inl 'igure I by a bar 93:).

Referring now to Figures 8 and 9, the control housing 95 is secured to the upper end of the casing III enclosing the final rotor drive shaft (see also Figure 6). The sprocket 62 is mounted in this housing on bearings 96 and is integral with a sleeve 81 having a quick pitch female thread 66 formed therein. This thread engages a corresponding male thread 69 formed on a bar M on which a. sleeve portion IIlIa integral with a link member III is rotatably but not slidably mounted by means of'bearings I62. The sleeve portion Ilia is slidably mounted in the housing 66 by means of bushes 96a.

The link member also carries a divided pivot pin I61, secured by means of a through-bolt III and nut I66, and having rotatably mounted thereon, by means of bearings III), a forked link III whose other end carries a spherical race II! enclosing two cages 01' balls I II running on races Ill carried by a cross-shaft H5 which is free to slide endways and to rotate. One end of shaft I I6 has splines H6 engaging corresponding splines of the sprocket 61, which is rotatably mounted in the housing 95 by means of bearings H1. The other end of shaft Iii has a male quick pitch thread "6 eng ing a corresponding female thread H6 in a sleeve III secured in the casing 85.

The link member IIiI also has formed thereon a spigot lllb carrying a male spherical element I63 engagin spherical seatings formed in a collar Ill and a nut I65 secured to the socket end ill of a lever 96 which is integral with the rotor axle member 36 (see Figures 2 and 6). (It will be remembered that the axle member I6 is supported on the gimbal mounting 34, I6 and has the hub 8i rotatably mounted on it.)

Fore and aft movement of thecontrol column causes the sprocket 92 to rotate by means of the operation of the intermediate elements 66, II, l2, 66, ll, 8|, 6i and the thread elements 96, 96 cause the bar I66 to move axially carrying with it the link member IBI, Ilia, Illlb, which thereby actuates the lever 64, I66 to tilt the axle member liandwithitthehub II intheforeandaft Similarly, transverse movement of the control column acting through the intermediate elements 16, 16. 16, II, 64, 86, ll rotates the sprocket l1 and shaft iii, which latter is caused bythetbreadelements Ill. Ill aisotoslideend- 8 waysandthismovestheforkedlink III torock the link member III, Illa. Illb transversely on its bearings II! and this in turn actuates the lever 66,166 to tilt the axle member 36 and with it the hub 3| inthe transverse plane.

The hub ii is driven by a ilnal drive shaft I2I through a universal joint I21, I26, a driven stud shaft I21, a spiined joint I", a driving plate I35 and a freewheel coupling I36. The details of this driving mechanism will not be further described as they form no part of the present invention.

An alternative construction for attaining the principal object of the invention, viz. the limitation of torsional/flapping characteristic to a small amplitude of blade displacement, while permitting more extended flapping displacement without further torsional displacement. is illustrated somewhat diagrammatically in Figures 10 to 15.

It must be understood that these figures are in no sense to be regarded as working drawings. but merely as illustrative of the functional relationships called for.

In these drawings parts strictly analogous to those already shown in Figures 2 to 5 and described with reference thereto are indicated by the same reference numbers but with the suflix 1'. Thus in Figures 10 and ii, a rotor supporting member 331:, 36.1: carries a gimbal ring 351:, which in turn supports the rotor axle member 361:, the gimbal ring being articulated to the members 34:, 35:: on trunnions 362:. The axle member 36:: rotatably supports the rotor hub 3 is, which is provided with ears 42.1: carrying drag pivot pins 2:, on which a drag link 46:: is rotatable for lead/lag displacement of the rotor blade.

The root end of the latter is indicated at It!) and is rotatable about its axis, for blade pitch varying displacement, on bearings I61 carried by a housing I62 (see also Figures 14, 15). The housing I62 has circular recesses I63 constituting bearings engaging inwardly projecting journal bosses I64 formed on side plates I65 interconnected by cross bars I13, I16 to form a cage member. The articulation I63, I constitutes the primary flapping pivot.

The torsional/flapping characteristic is obtained by means of a collar I86 embracing the blade root I66 and engaging splines I61 thereon which lock the collar against rotation, but permit it to be shifted along the blade root for adjusting the ratio of pitch change to flappin a stud I66 secures the collar I66 in the desired position. The collar I66 carries a spigot I86 carrying (rotatably) a bead I16 engaging a slot "I in an arm I12 secured to cage member I65, I13, I16. Arm I12 lies on the leading side of the blade and hence upward flapping of the blade on the articulation I63, I66 causes decrease of pitch angle in the same way as the similar mechanism already described with reference to Figures 2 to 5. The torsional/flapping displacement is limited by the blade root I engaging the upper or the lower of the cross bars I13.

More extended flapping without torsional characteristic is accommodated by a "lever articulation" comprising two pairs of fulcrum pins I14 projecting from the side plates I of the cage member I65, I13, I16, the pairs of fulcrum pins being located respectively above and below the axis of the blade and engaging elongated slots I16 formed in the drag link 660:.

As long as flapping does not exceed the amplitude permitted by the stop bars I". it takes place entirely about the articulation I63, itl because the centrifugal force of the blade holds both pairs of fulcrum pins against the outboard ends of slots I'll, but any further flapping is accommodated by rocking of the cage I68, H3, H8 on either the lower or upper pair of fulcra I'll, I15, according as the flapping is upward or downward. and such further flapping is resisted by a considerable centrifugal moment. It is not accommodated by any further torsional displacement of the blade, because the cage member I85, I'll, lit to which the arm "2 is secured now participates in the flapping and the arm in therefore follows the blade and has no further action on the torsion lever I66, I89.

The more extended flapping displacement is finally limited by the length of the slots I15, which defines the possible travel of the fulcrum pins I'll.

The two modes of flapping displacement are illustrated diagrammatically in Figures 16 to 18, in which no attempt has been made to give the parts (indicated by reference numbers corresponding to those of Figures 10 to their proper shape, but merely their relative positions.

Figure 17 shows the mean position of the blade in full line and the limits of upward and downward flapping (with torsional displacement), on the primary flapping articulation, in dotted lines. Figures 16 and 18 show respectively the ultimate limiting positions for upward and downward flapping in which the "lever articulation is involved.

What I claim is:

1. In an aircraft having a hub, a rotative sustaining blade, and articulated means connecting the blade to the hub including torsional pivot means and flapping pivot means, the combination which includes: a lever mounted to react between the blade and the articulated means in a limited range of blade movement to alter the pitch of the blade when the blade moves in the flapping plane relative to said lever means, and pitch limit stop means forming a part of the articulated means and positioned to be actuated by movement of the blade beyond said limited range of movement, said stop means being connected to said lever to constrain the latter to move simultaneously with the former.

2. In a helicopter including a rotor hub, a lifting rotor blade, and articular means connecting the blade to the hub including pivotal means about (which pitch-changing movement and flapping movement of the blade take place, the combination which includes means reacting between the blade and the articular means to cause pitch-changing movement of the blade simultaneously with flapping movement of the blade within a predetermined range of such flapping movement, and means eifective to impose a restraint upon the operation of said pitchchanging means when flapping movement exceeds said predetermined range, said last named means incorporating a lost-motion connection between the articular means and the pitchchanging means accommodating pitch-changing movement within said predetermined range.

3. A device as set forth in claim 2, in which the means eifective to impose a restraint comprises fulcrum means positioned to be selectively operated upon movement of the blade beyond the predetermined range or flapping movement.

4. In a helicopter including a rotor hub and a lifting rotor blade. articular means connecting the blade to the hub comprising an intermediate blade supporting member, pivot means connectlng the supporting member to the hub and permitting movement of the blade substantially in the flapping plane containing the radial blade axis and the hub axis, pivot means connecting the blade to the supporting member and permitting torsional movement of the blade about its radial axis, stop means on the supporting member limitin torsional movement of the blade from its mean position, linkage reacting between the blad: and a portion of the articular means and en: uring coordinated flapping displacement of the blade and supporting member about the first named pivot means and torsional displacement of the blade on the supporting member about the second named pivot means in the sense that upward flapping is accompanied by decrease in pitch angle, within the limits of torsional displacement imposed by the said stop means; and yieldable means interconnecting said firstnamed pivot means and said linkage and accommodating flappin displacement beyond said limits without further torsional displacement of the blade.

5. In a helicopter including a rotor hub and a lifting rotor blade, articular means connecting the blade to the hub comprising an intermediate blade supporting member, pivot mechanism connecting the blade to the supporting member and accommodatin flapping and torsional displacements of the blade, a supplemental connection between said blade and a part of the pivot mechanism about which flapping displacements of the blade take place, said connection being mounted to cause torsional displacement of the blade in a sense to decrease pitch angle on upward flapping and vice versa, stop means forming a part of said pivot mechanism, positioned to limit the range of blade displacement in a flapping sense relative to said supplemental connection, and pivotal means connecting the supporting member to the hub and providing for greater displacement of the blade substantially in the flapping plane containing the radial blade axis and the rotor hub axis, said last named pivotal means having a yieldable coupling locking the supporting member and the hub against relative movement thereon by the action of centrifugal force transmitted from the blade except when the blade has reached either limit of displacement, about the first named pivot means, imposed by the said step means.

6. In a helicopter including a rotor hub, a lifting rotor blade, and articular means connecting the blade to the hub including pivotal means about which pitch-changing movement and flapping movement of the blade take place, the combination which includes an auxiliary connection between the blade and the articular means, mounted to move with the blade through a substantial portion of the path of flapping movement, and a lost-motion device interposed between said connection and said articular means providing relative movement between blade and connection within the limits of such lost-motion. the blade and the connection being inter-connected to effect an alteration in pitch angle of the latter only when relative movement between blade and connection occurs.

'7. A helicopter as claimed in claim 5, wherein the last named pivotal means include two pivots with parallel axes lying respectively above and below the mean radial axis of the blade. abutments for said pivots so placed as to resist the centrifugal force transmitted from the blade and clearances permitting separation of said pivots from their abutments at least to a limited exten 8. A helicopter as claimed in claim 4, wherein the mentioned restraining means comprise a lever secured to the blade and extending iorwardiy therei'rom in the direction rotation oi the blade, an arm disposed substantially parallel to the blade and having its outboard end universally Jointed to the forward end oi said lever, the inboard end 01' said arm being rotatably mounted about the axis of the first named pivot means and the mentioned yieldable means comprise springloaded clutch means interposed between the inboard end 0! said arm and the hub, whereby the arm is locked to the hub as long as the blade is free to move on the second named pivot means relatively to the supporting'member but, on the blade reaching either 01' the stop means limiting movement on said second named pivot means, yielding or the spring loading takes place allowing the clutch means to slip, thereby rendering the torsional-flapping restraining means inoperative, so that greater displacement of the blade and supporting member about the first named pivot means can take place without further displacement on the second named torsional pivot means, such displacement being prevented by the stop means. 9. In a helicopter as claimed in claim 4, the inclusion of a second intermediate member articulated to the hub by a drag pivot, permitting lead and lag displacement of the blade, the first mentioned intermediate blade supporting member being connected to the last named intermediate member by the first named pivot means.

10. In a helicopter as claimed in claim 5, the inclusion of a second intermediate member articulated to the hub by a "drag'? pivot, permitting lead and lag displacement of the blade. the first mentioned intermediate blade supporting member being connected to the last named intermediate member by the second named pivotal means of claim 5.

ll.linahelicopterinciudingarotorhub,a lifting rotor blade, and articular means connecting the blade to the hub including pivotal means about which pitch-changing movement and flapping movement 0! the blade takes place, the combination which includes means reacting between the blade and the articular means to cause pitch-changing movement 01' the blade simultaneously with flapping movement or the blade within a predetermined range of such flapping movement, and means eilective to impose a restraint upon the operation of said pitch-changing means when'fiapping movement exceeds said predetermined range, said restraint imposing means comprising cam structures mounted in fixed relation to the blade means and to the hub means, respectively, and a yieldable connection between said cam structures.

CYRIL GEORGE Pm.

REFERENCES CITED The following references are of record in th tile 0! this patent: 8

UNITED STATES PATENTS Number Name Date 1,948,457 Larsen Feb. 20, 1934 1,950,080 De La Cierva Mar. 6, 1934 1,971,016 Pecker Aug. 21, 1934 2,108,417 Stanley Feb. 15, 1938 2,318,259 Sikorsky May 4, 1943 2,330,842 Puilin Oct. 5, 1943 2,365,357 Prewitt Dec. 19, 1944 2,380,582 De in Glens. July 31, 1945 FOREIGN PATENTS Number Country Date 476,596 Great Britain Dec. 13, 1937 

